(Radiographics. 2000;20:333-352.)
© RSNA, 2000
Painful Heel: MR Imaging Findings1
José A. Narváez, MD,
Javier Narváez, MD ,
Raúl Ortega, MD ,
Carlos Aguilera, MD ,
Ana Sánchez, MD and
Eduard Andía, MD
1 From the Department of CT and MRI-Institut de Diagnòstic per la Imatge (J.A.N., R.O., C.A., A.S., E.A.) and the Department of Rheumatology (J.N.), Hospital Duran Reymals, Ciutat Sanitària y Universitària de Bellvitge, Autovía de Castelldefels km 2'7, L'Hospitalet de Llobregat, 08907 Barcelona, Spain. Recipient of a Certificate of Merit award for a scientific exhibit at the 1998 RSNA scientific assembly. Received February 25, 1999; revision requested April 7 and received May 24; accepted May 24. Address reprint requests to J.A.N. (e-mail: cvalls@csub.scs.es).
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Abstract
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Heel pain is a common and frequently disabling clinical complaint that may be caused by a broad spectrum of osseous or soft-tissue disorders. These disorders are classified on the basis of anatomic origin and predominant location of heel pain to foster a better understanding of this complaint. The disorders include plantar fascial lesions (fasciitis, rupture, fibromatosis, xanthoma), tendinous lesions (tendinitis, tenosynovitis), osseous lesions (fractures, bone bruises, osteomyelitis, tumors), bursal lesions (retrocalcaneal bursitis, retroachilleal bursitis), tarsal tunnel syndrome, and heel plantar fat pad abnormalities. With its superior soft-tissue contrast resolution and multiplanar capability, magnetic resonance (MR) imaging can help determine the cause of heel pain and help assess the extent and severity of the disease in ambiguous or clinically equivocal cases. Careful analysis of MR imaging findings and correlation of these findings with patient history and findings at physical examination can suggest a specific diagnosis in most cases. The majority of patients with heel pain can be successfully treated conservatively, but in cases requiring surgery (eg, plantar fascia rupture in competitive athletes, deeply infiltrating plantar fibromatosis, masses causing tarsal tunnel syndrome), MR imaging is especially useful in planning surgical treatment by showing the exact location and extent of the lesion.
Index Terms: Ankle, anatomy, 46.92 • Ankle, MR, 46.12141, 46.121413, 46.121415, 46.121416 • Bones, infection, 46.21 • Bursitis, 46.251 Calcaneus, fractures, 4642.41 • Foot, anatomy, 46.92 • Foot, MR, 46.12141 • Tendinitis, 46.253 • Tenosynovitis, 46.252
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Introduction
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Heel pain, or calcaneodynia, is a frequent symptom in patients with foot and ankle disorders. This complaint may cause significant disability and interfere with routine activities. Clinical diagnosis of the cause of pain is often difficult due to the broad spectrum of potential causes.
Heel pain may arise from six major anatomic structures: (a) the plantar fascia, (b) various tendons (Achilles tendon, flexor digitorum longus [FDL] tendon, flexor hallucis longus [FHL] tendon), (c) the calcaneus, (d) bursae (retrocalcaneal bursa, retroachilleal bursa), (e) the tarsal tunnel and its nerve content, and (f) the heel plantar fat pad (Fig 1).
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Figure 1a. Major anatomic structures of the heel. (a) Diagram shows the location of the retrocalcaneal and retroachilleal bursae, Achilles tendon, and plantar fascia and their relationship to the calcaneus. (b) Diagram shows the normal anatomy of the tarsal tunnel. The posterior tibial and FDL tendons and the posterior tibial nerve course under the flexor retinaculum. The posterior tibial vascular bundle and FHL tendon (not shown) run adjacent to the posterior tibial nerve. Distal to the flexor retinaculum, the abductor hallucis muscle overlies the terminal branches of the posterior tibial nerve.
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Figure 1b. Major anatomic structures of the heel. (a) Diagram shows the location of the retrocalcaneal and retroachilleal bursae, Achilles tendon, and plantar fascia and their relationship to the calcaneus. (b) Diagram shows the normal anatomy of the tarsal tunnel. The posterior tibial and FDL tendons and the posterior tibial nerve course under the flexor retinaculum. The posterior tibial vascular bundle and FHL tendon (not shown) run adjacent to the posterior tibial nerve. Distal to the flexor retinaculum, the abductor hallucis muscle overlies the terminal branches of the posterior tibial nerve.
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Magnetic resonance (MR) imaging allows direct, noninvasive depiction of all osseous and soft-tissue structures of the hindfoot by virtue of its superior soft-tissue contrast resolution and multiplanar capability. Therefore, in ambiguous or clinically equivocal cases, MR imaging can help determine the cause of heel pain and help assess the extent and severity of the disease.
In this article, we review the normal anatomy of the foot and ankle as well as the clinical and radiologic manifestations of a variety of painful conditions of the heel that are classified according to anatomic origin. We also review pertinent MR imaging findings with emphasis on those findings that suggest a specific diagnosis.
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Plantar Fascial Lesions
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The plantar fascia is a multilayered, fibrous aponeurosis with medial, central, and lateral components (1). The term plantar fascia typically refers to the large central component, which originates from the medial calcaneal tuberosity and extends anteriorly, adhering to the underlying flexor digitorum brevis (FDB) muscle. At about the midsole, it splits into five bands, one for each toe, that insert on the proximal phalanges.
The medial and lateral components of the plantar fascia act mainly as covering layers peripheral to the central component. The medial component serves as the fascial covering for the abductor hallucis muscle, and the lateral component, which originates from the lateral margin of the medial calcaneal tuberosity, forms the investing fascia of the abductor digiti minimi muscle.
The plantar fascia acts as a strong mechanical tie for the longitudinal arches by joining the three main weight-bearing points of the foot: the calcaneus, the first metatarsal head (including the two sesamoid bones), and the fifth metatarsal head (1).
At MR imaging, the normal fascia appears as a thin (2–4-mm) band with low signal intensity with all pulse sequences (Fig 2) (2–4).
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Figure 2a. Normal plantar fascia. (a) Sagittal T1-weighted (repetition time msec/echo time msec = 450/25) MR image shows the plantar fascia (arrows) as a low-signal-intensity structure extending anteriorly from the medial tuberosity of the calcaneus. Note the course of the FHL tendon (fhl) under the sustentaculum tali (ST). Insertion of the Achilles tendon (a) on the posterior aspect of the calcaneus is also seen. (b) Coronal T1-weighted (450/25) MR image demonstrates the three components of the plantar fascia. The central component is the structure referred to as the plantar fascia (white arrow), and its fibers adhere to the underlying FDB muscle (fd). The medial (black arrows) and lateral (arrowheads) components represent the investing fascia of the abductor hallucis (ah) and abductor digiti minimi (adm) muscles, respectively. Note the quadratus plantae muscle (qp) adjacent to the medial aspect of the calcaneus (C).
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Figure 2b. Normal plantar fascia. (a) Sagittal T1-weighted (repetition time msec/echo time msec = 450/25) MR image shows the plantar fascia (arrows) as a low-signal-intensity structure extending anteriorly from the medial tuberosity of the calcaneus. Note the course of the FHL tendon (fhl) under the sustentaculum tali (ST). Insertion of the Achilles tendon (a) on the posterior aspect of the calcaneus is also seen. (b) Coronal T1-weighted (450/25) MR image demonstrates the three components of the plantar fascia. The central component is the structure referred to as the plantar fascia (white arrow), and its fibers adhere to the underlying FDB muscle (fd). The medial (black arrows) and lateral (arrowheads) components represent the investing fascia of the abductor hallucis (ah) and abductor digiti minimi (adm) muscles, respectively. Note the quadratus plantae muscle (qp) adjacent to the medial aspect of the calcaneus (C).
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The plantar fascia is best evaluated with sagittal and coronal MR imaging. The coronal plane represents the true axial plane perpendicular to the plantar fascia, and coronal imaging is optimal for assessing the size, shape, and internal signal characteristics of this structure. On coronal images, the inferior edge of the fascia is straight and contrasts sharply with adjacent fat. Sagittal imaging allows optimal evaluation of the plantar fascia along its length. On sagittal images, the normal fascia has a uniform thickness from its calcaneal origin through its proximal half, whereas more distally it progressively thins until it reaches its metatarsal insertions (4). Standard imaging protocol in the evaluation of the plantar fascia includes (a) sagittal T1-weighted images along with short-inversion-time inversion recovery (STIR) images or fat-suppressed conventional spin-echo or fast spin-echo T2-weighted images, and (b) coronal proton-density–weighted and T2-weighted conventional spin-echo or fast spin-echo images.
Plantar Fasciitis
Plantar fasciitis is the most common cause of plantar heel pain (5). This condition can arise either from the stress of repetitive trauma or as an enthesopathy in association with seronegative spondyloarthropathies (ankylosing spondylitis, Reiter syndrome, psoriatic arthritis) (5,6).
The stress-related form of plantar fasciitis is more common and generally occurs in obese middle-aged or elderly patients as a result of repetitive trauma from athletic activities, excessive job-related standing and walking, changes in walking surfaces, or changes in shoewear (5,7). It may also occur in young persons who engage in sports activities that involve running or jumping. In these situations, microtears occur, mainly in the origin of the plantar fascia, and elicit a local inflammatory reaction (5,7).
Pain on the undersurface of the heel on weight bearing is the principal complaint. The pain is often worse when weight is borne after a period of rest (eg, in the morning) and eases with walking. Localized tenderness without swelling is present over the anteromedial portion of the plantar surface of the calcaneus. Passive dorsiflexion of the toes often exacerbates the discomfort.
Radiography may reveal a plantar calcaneal spur, although this entity may also be observed in asymptomatic adults (5,7). The etiologic significance of this spur remains controversial, but most authors believe that it is not the primary cause of pain (5,7).
MR imaging characteristics of plantar fasciitis include (a) fascial thickening that is often fusiform and typically involves the proximal portion and extends to the calcaneal insertion (2,3), and (b) increased signal intensity of the proximal plantar fascia, which demonstrates intermediate signal intensity on T1-weighted or proton-density–weighted images and high signal intensity on T2-weighted or STIR images (Fig 3). Other MR imaging findings that indicate plantar fasciitis include edema of the adjacent fat pad and underlying soft tissues and limited marrow edema within the medial calcaneal tuberosity (4). STIR MR imaging is often the most sensitive in the detection of both fascial and perifascial edema, which appear as poorly marginated areas of high signal intensity.
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Figure 3a. Plantar fasciitis in a 60-year-old woman. Sagittal T1-weighted (590/25) (a) and STIR (2,416/20; inversion time msec = 160) (b) MR images show marked thickening of the proximal plantar fascia (large arrows) with increased intrasubstance signal intensity (small arrows). Note also the perifascial edema, which has low signal intensity in a and high signal intensity in b (arrowheads).
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Figure 3b. Plantar fasciitis in a 60-year-old woman. Sagittal T1-weighted (590/25) (a) and STIR (2,416/20; inversion time msec = 160) (b) MR images show marked thickening of the proximal plantar fascia (large arrows) with increased intrasubstance signal intensity (small arrows). Note also the perifascial edema, which has low signal intensity in a and high signal intensity in b (arrowheads).
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Plantar fasciitis related to seronegative spondyloarthropathies is usually bilateral (3,6) and is often associated with Achilles tendinitis and retrocalcaneal bursitis. Fascial and edematous changes are more prominent (4), and there are greater bone marrow edema changes within the subcortical region of the medial calcaneal tuberosity.
Successful outcome is directly related to early diagnosis and treatment (7).
Treatment is conservative and consists of weight reduction in obese patients, rest, nonsteroidal antiinflammatory drug therapy, local steroid injection, and reduction of weight-bearing pressure with a soft rubber heel pad, molded orthosis, or heel cup or soft-soled shoes (5,7). No more than two local corticosteroid injections are recommended due to concerns about steroid-induced plantar fascia rupture and atrophy of the heel pad (5,7–9).
Surgical treatment of plantar fasciitis is reserved for cases in which conservative treatment fails (5, 7), especially in athletes engaged in high-level competition.
Plantar Fascia Rupture
Rupture of the plantar fascia is typically a sports-related injury, particularly in athletes engaged in sports that require running and jumping such as distance running, basketball, football, and tennis (9–11). However, it can also be associated with local corticosteroid injection in patients with plantar fasciitis (8).
Sudden plantar heel pain typically indicates a traumatic tear. The individual usually hears a clicking or snapping sound when the traumatic event occurs (9,12), and a palpable, tender mass is detected at the site of injury. Clinical manifestations in patients with tears related to corticosteroid injection are more insidious (8).
Most cases of plantar fascia rupture involve the proximal portion of the fascia near its calcaneal insertion, although more anterior tears have also been described (1,4,11,13).
MR imaging findings in plantar fascia tears are similar to those seen in tendinous ruptures. Acute tears of the plantar fascia are characterized by partial or complete interruption of the normally low-signal-intensity fascia by large areas of markedly increased signal intensity on T2-weighted and STIR images, presumably representing edema and hemorrhage (Fig 4) (4,9,12,13). Perifascial fluid accumulations with high signal intensity are commonly seen on T2-weighted images. In addition, tears of the plantar fascia commonly involve the underlying FDB muscle (Fig 4) (4,12). Acute and subacute muscle tears are characterized by high-signal-intensity changes with a feathery appearance on both T1- and T2-weighted images representing muscle bleeding and edema. Less commonly, strains of other plantar muscles such as the abductor hallucis or quadratus plantae muscle are associated with plantar fascia rupture (4,12). Conservative treatment consisting of rest, shoe arch supports and orthoses, and physical therapy is sufficient in most cases (8,9,11).
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Figure 4a. Plantar fascia rupture in a 22-year-old professional basketball player. (a) Coronal proton-density-weighted (1,800/20) MR image shows a defect of the right plantar fascia representing a tear (black arrow). The underlying FDB muscle also demonstrates changes in signal intensity representing edema and hemorrhage (white arrows). (b) Corresponding coronal T2-weighted (1,800/90) MR image depicts the aponeurotic defect (black arrow). The associated lesion of the underlying FDB muscle has ill-defined high signal intensity (white arrows).
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Figure 4b. Plantar fascia rupture in a 22-year-old professional basketball player. (a) Coronal proton-density-weighted (1,800/20) MR image shows a defect of the right plantar fascia representing a tear (black arrow). The underlying FDB muscle also demonstrates changes in signal intensity representing edema and hemorrhage (white arrows). (b) Corresponding coronal T2-weighted (1,800/90) MR image depicts the aponeurotic defect (black arrow). The associated lesion of the underlying FDB muscle has ill-defined high signal intensity (white arrows).
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Plantar Fibromatosis
Plantar fibromatosis is a relatively uncommon benign but locally invasive lesion that is characterized by fibrous proliferation arising from the plantar fascia (14). It can be associated with other superficial fibromatoses, mainly with palmar fibromatosis (14). At clinical examination, plantar fibromatosis is characterized by fibrous nodules in the plantar arch with frequent bilateral involvement. Typically, these nodules are painless or cause only vague or perhaps moderate pain. Fascial scarring and contracture may be seen late in the disease course. Diagnosis is made with palpation of plantar nodules.
Plantar fibromatosis usually involves the central and medial portions of the plantar fascia, although it can also affect the proximal portion (13,15). Radiographic findings are usually normal. MR imaging is considered the modality of choice in the assessment of plantar fibromatosis (14). Lesions appear as single or multiple nodular areas of thickening of the inferior margin of the plantar fascia (15). These nodules have low to intermediate signal intensity on T1- and T2-weighted images, probably due to the relative acellularity and high collagen content of the lesions. Larger lesions tend to have heterogeneous signal intensity (Fig 5). Infiltration of the plantar musculature can be seen due to the aggressive nature of this condition (15).
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Figure 5a. Plantar fibromatosis in a 60-year-old man. (a) Coronal proton-density-weighted (1,800/20) MR image demonstrates three nodules arising from the plantar fascia. The largest lesion (arrowheads) is heterogeneous and slightly hyperintense relative to adjacent muscle with small regions of low signal intensity. The other two nodules have homogeneous low signal intensity (arrows). (b) On a corresponding T2-weighted (1,800/90) MR image, the two small lesions remain hypointense (arrows), whereas the largest lesion (arrowheads) shows decreased signal intensity but remains slightly hyperintense relative to adjacent muscle.
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Figure 5b. Plantar fibromatosis in a 60-year-old man. (a) Coronal proton-density-weighted (1,800/20) MR image demonstrates three nodules arising from the plantar fascia. The largest lesion (arrowheads) is heterogeneous and slightly hyperintense relative to adjacent muscle with small regions of low signal intensity. The other two nodules have homogeneous low signal intensity (arrows). (b) On a corresponding T2-weighted (1,800/90) MR image, the two small lesions remain hypointense (arrows), whereas the largest lesion (arrowheads) shows decreased signal intensity but remains slightly hyperintense relative to adjacent muscle.
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Treatment is initially conservative, but surgery is indicated in patients with painful or deep infiltrating lesions. Because of the high rate of postsurgical recurrence, use of complementary radiation therapy or chemotherapy with methotrexate has been advocated (14).
Plantar Fascia Xanthoma
Xanthomas are a prominent feature of several types of primary hyperlipidemias and consist of localized collections of tissue histiocytes containing lipids, most frequently in the skin and subcutis. Tendon xanthomas can be observed in patients with type IIa or III hyperlipoproteinemia.
Tendon xanthomas are usually bilateral and symmetric. They are typically seen over the finger extensors in the dorsum of the hands and, less frequently, over the Achilles tendons near their insertion on the calcanei (16–19). The plantar fascia is occasionally infiltrated, and the extensor tendons of the toes are more rarely involved (19). Plantar fascia xanthomas are usually asymptomatic, although in some cases they produce vague pain (16–19) and undesirable cosmetic effects.
At radiography, tendinoaponeurotic xanthomas appear as soft-tissue masses without calcification. MR imaging shows fusiform tendinous or aponeurotic enlargement with heterogeneous signal intensity (17–19). Small foci of increased tendinous signal intensity corresponding to the xanthomatous deposits, along with trabeculated low-signal-intensity areas representing the remaining tendinous fascicles, produce a characteristic speckled or reticulated appearance on both T1- and T2-weighted images (Fig 6) (17–19).
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Figure 6a. Xanthomas of the plantar fascia and Achilles tendon in a 56-year-old woman. (a) Sagittal T1-weighted (450/25) MR image demonstrates fusiform thickening of the plantar fascia (arrows) and Achilles tendon (arrowheads) with a speckled pattern of increased signal intensity. (b) Coronal T1-weighted (450/25) MR image shows fusiform enlargement of the plantar fascia (arrows). Note the globular, heterogeneous pattern of increased signal intensity representing the xanthomatous deposit and the interspersed areas of low signal intensity representing residual normal collagen fibers. (c) On a corresponding T2-weighted (1,800/90) MR image, the increased signal intensity of the aponeurotic xanthoma is less evident (arrows).
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Figure 6b. Xanthomas of the plantar fascia and Achilles tendon in a 56-year-old woman. (a) Sagittal T1-weighted (450/25) MR image demonstrates fusiform thickening of the plantar fascia (arrows) and Achilles tendon (arrowheads) with a speckled pattern of increased signal intensity. (b) Coronal T1-weighted (450/25) MR image shows fusiform enlargement of the plantar fascia (arrows). Note the globular, heterogeneous pattern of increased signal intensity representing the xanthomatous deposit and the interspersed areas of low signal intensity representing residual normal collagen fibers. (c) On a corresponding T2-weighted (1,800/90) MR image, the increased signal intensity of the aponeurotic xanthoma is less evident (arrows).
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Figure 6c. Xanthomas of the plantar fascia and Achilles tendon in a 56-year-old woman. (a) Sagittal T1-weighted (450/25) MR image demonstrates fusiform thickening of the plantar fascia (arrows) and Achilles tendon (arrowheads) with a speckled pattern of increased signal intensity. (b) Coronal T1-weighted (450/25) MR image shows fusiform enlargement of the plantar fascia (arrows). Note the globular, heterogeneous pattern of increased signal intensity representing the xanthomatous deposit and the interspersed areas of low signal intensity representing residual normal collagen fibers. (c) On a corresponding T2-weighted (1,800/90) MR image, the increased signal intensity of the aponeurotic xanthoma is less evident (arrows).
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Lowering of serum cholesterol levels can lead to a decrease in the size of tendon xanthomas. Surgical excision has provided long-lasting relief in a few patients, although recurrence has been noted in some cases (16).
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Tendinous Lesions
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Insertional Achilles Tendinitis
The Achilles tendon is formed by the union of the tendons of the gastrocnemius and soleus muscles and inserts on the posterior aspect of the calcaneus. It is not invested by a synovial sheath, but is surrounded by loose connective tissue referred to as the peritenon. At MR imaging, the Achilles tendon has uniformly low signal intensity and a flattened or slightly concave anterior border and is usually less than 1 cm in anteroposterior thickness.
Achilles tendinitis involving the calcaneal insertion of the tendon is known as insertional Achilles tendinitis and is one of the main causes of posterior heel pain (13). This condition is usually caused by repetitive trauma and microscopic tears due to excessive use of the calf muscles. It is seen most frequently in ballet dancers, runners, and athletes engaged in sports that involve jumping. It may also be seen in patients with rheumatoid arthritis and seronegative spondyloarthropathies (13).
Insertional Achilles tendinitis is characterized by posterior heel pain along with swelling and tenderness over the tendon near its insertion (13). Passive dorsiflexion of the ankle intensifies the pain. MR imaging shows thickening of the tendon at its insertion (3,13) with loss of the normal concavity of its anterior margin. Intratendinous areas of increased signal intensity are seen on T1-weighted and proton-density–weighted MR images (Fig 7) but are less evident or even absent on T2-weighted images. At MR imaging, Achilles tendinitis related to rheumatoid arthritis is characterized by the absence of tendinous enlargement and association with retrocalcaneal bursitis (20).
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Figure 7a. Achilles tendinitis in a 34-year-old long-distance runner. Sagittal T1-weighted (590/25) (a) and STIR (2,416/20/160) (b) MR images demonstrate diffuse thickening of the Achilles tendon throughout its length (arrows) with minimal intratendinous foci of increased signal intensity.
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Figure 7b. Achilles tendinitis in a 34-year-old long-distance runner. Sagittal T1-weighted (590/25) (a) and STIR (2,416/20/160) (b) MR images demonstrate diffuse thickening of the Achilles tendon throughout its length (arrows) with minimal intratendinous foci of increased signal intensity.
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Inflammation of the peritenon, or peritendinitis, may precede or be associated with insertional Achilles tendinitis. MR imaging shows a loss of normal high signal intensity of peritendinous fat, with ill-defined reticulated areas of decreased signal intensity on T1-weighted images. The increased signal intensity seen on T2-weighted images represents inflammatory and edematous changes. Treatment consists of rest, avoidance of the provocative occupational or athletic activity, shoe modification, heel elevation to reduce tendon stretching during walking, nonsteroidal antiinflammatory drug therapy, and physical therapy.
Corticosteroid injections in or near the tendon are of questionable value. They predispose patients to tendon rupture and should be discouraged.
Tendinitis and Tenosynovitis of the FDL and FHL Tendons
The FDL and FHL tendons course through the posteromedial ankle. The FDL tendon lies just posterolateral to the posterior tibial tendon, running posterior to the talus. The FHL tendon courses posterolateral to the posterior tibial tendon and the FDL tendon, running through a shallow groove in the posteromedial aspect of the talus between the lateral and medial processes; it then continues distally under the sustentaculum tali. On the plantar aspect of the heel, the FHL tendon crosses deep to the FDL tendon, and both course along the plantar aspect of the sole. The FDL tendon inserts on the bases of the second through the fifth distal phalanges, and the FHL tendon inserts on the great toe. At MR imaging, these tendons demonstrate homogeneous low signal intensity with all pulse sequences; they are best evaluated with oblique axial imaging perpendicular to the long axis of the tendon and with sagittal imaging.
Tendinitis and tenosynovitis of either the FHL tendon (5,21) or (less commonly) the FDL tendon may also cause posteromedial heel pain. Athletes who perform repetitive forceful pushoffs with the forefoot (eg, ballet dancers) are predisposed to FHL tenosynovitis (3,21).
Tenosynovitis is characterized by a considerable amount of synovial fluid causing distention of the tendinous sheath. This condition demonstrates decreased signal intensity on T1-weighted MR images and increased signal intensity on T2-weighted images surrounding the low-signal-intensity tendon (Fig 8).
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Figure 8a. FHL tenosynovitis in an 18-year-old girl. (a) Sagittal STIR (2,416/20/160) MR image shows fluid distending the synovial sheath of the FHL tendon (arrows). (b) Axial T2-weighted (2,500/90) MR image demonstrates hyperintense synovial fluid within the sheath of the FHL tendon (flh, arrows). Because the sheath of this tendon communicates with the ankle joint in 20% of patients, the diagnosis of tenosynovitis requires a disproportionate amount of fluid within the sheath. Note the adjacent course of the FDL tendon (fdl) and the small, physiologic amount of synovial fluid within its sheath.
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Figure 8b. FHL tenosynovitis in an 18-year-old girl. (a) Sagittal STIR (2,416/20/160) MR image shows fluid distending the synovial sheath of the FHL tendon (arrows). (b) Axial T2-weighted (2,500/90) MR image demonstrates hyperintense synovial fluid within the sheath of the FHL tendon (flh, arrows). Because the sheath of this tendon communicates with the ankle joint in 20% of patients, the diagnosis of tenosynovitis requires a disproportionate amount of fluid within the sheath. Note the adjacent course of the FDL tendon (fdl) and the small, physiologic amount of synovial fluid within its sheath.
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Repetitive acute tenosynovitis progresses to stenosing tenosynovitis, a chronic condition characterized by the formation of fibrous or scar tissue in the tendinous sheath that interferes with tendon gliding (21). These fibrous changes appear as an intermediate-signal-intensity rind surrounding the tendon on both T1- and T2-weighted images.
Tendinitis is characterized by variable tendinous thickening with increased signal intensity on T1-weighted or proton-density–weighted MR images. Tendinous signal intensity is normal or only slightly increased on T2-weighted images.
Treatment is conservative and includes rest, nonsteroidal antiinflammatory drug therapy, and physical therapy. Surgical release of the FHL tendon is performed if conservative treatment fails (21).
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Osseous Lesions
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Fractures
Stress Fracture.—Stress fractures may be divided into fatigue-type fractures (ie, fracture of normal bone from unusual stress) and insufficiency-type fractures (ie, fracture of abnormal bone with normal stress).
After the metatarsal bones, the calcaneus is the second most frequent location of fatigue-type stress fractures of the foot. These fractures may be observed in athletes engaged in sports that involve jumping and running.
Insufficiency-type stress fractures of the calcaneus are observed in patients with rheumatoid arthritis and neurologic disorders. Osteoporosis, which is commonly seen in patients with chronic rheumatoid arthritis, and abnormal mechanical stress caused by rheumatoid deformities may cause stress fractures. Constant pain, disability, and rheumatoid deformities may obscure the diagnosis in these patients. The antagonistic action of the plantar fascia and Achilles tendon, which is intensified in neurologic disorders characterized by spastic muscular tension, also results in insufficiency fractures.
Stress fractures generally involve the posterosuperior or posterior calcaneus and have a vertical orientation. Patients typically complain of diffuse heel pain and tenderness over the medial and lateral aspects of the heel (3,5,7,13). Radiographic findings are usually normal in the early stages (13,22), and follow-up radiography discloses diagnostic features in only 50% of cases (23). MR imaging demonstrates characteristic findings that include (a) bandlike areas of very low signal intensity in the medullary space, which usually extend to the cortex, and (b) surrounding alteration in signal intensity in the marrow space with ill-defined low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, which represents medullary edema and hemorrhage (Fig 9) (22,23).
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Figure 9a. Stress fracture in a 65-year-old man who presented with heel pain after completing a 2-week program of vigorous aerobic exercise. (a) Radiograph shows only a faint sclerotic band in the posterior region of the calcaneus (arrowheads). (b) Sagittal T1-weighted (450/25) MR image shows a low-signal-intensity band in the posterior region of the calcaneus (arrowheads) representing the fracture line. Associated diffuse bone marrow edema of the calcaneus demonstrates ill-defined low signal intensity. (c) Axial T2-weighted (2,500/90) MR image clearly depicts the irregular hypointense fracture line parallel to the posterior cortical margin (arrowheads). The associated diffuse bone marrow edema of the calcaneus has high signal intensity (cf b). (d) Follow-up radiograph obtained 3 weeks later shows a more evident band of new bone formation (arrowheads) corresponding to the abnormality seen at MR imaging.
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Figure 9b. Stress fracture in a 65-year-old man who presented with heel pain after completing a 2-week program of vigorous aerobic exercise. (a) Radiograph shows only a faint sclerotic band in the posterior region of the calcaneus (arrowheads). (b) Sagittal T1-weighted (450/25) MR image shows a low-signal-intensity band in the posterior region of the calcaneus (arrowheads) representing the fracture line. Associated diffuse bone marrow edema of the calcaneus demonstrates ill-defined low signal intensity. (c) Axial T2-weighted (2,500/90) MR image clearly depicts the irregular hypointense fracture line parallel to the posterior cortical margin (arrowheads). The associated diffuse bone marrow edema of the calcaneus has high signal intensity (cf b). (d) Follow-up radiograph obtained 3 weeks later shows a more evident band of new bone formation (arrowheads) corresponding to the abnormality seen at MR imaging.
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Figure 9c. Stress fracture in a 65-year-old man who presented with heel pain after completing a 2-week program of vigorous aerobic exercise. (a) Radiograph shows only a faint sclerotic band in the posterior region of the calcaneus (arrowheads). (b) Sagittal T1-weighted (450/25) MR image shows a low-signal-intensity band in the posterior region of the calcaneus (arrowheads) representing the fracture line. Associated diffuse bone marrow edema of the calcaneus demonstrates ill-defined low signal intensity. (c) Axial T2-weighted (2,500/90) MR image clearly depicts the irregular hypointense fracture line parallel to the posterior cortical margin (arrowheads). The associated diffuse bone marrow edema of the calcaneus has high signal intensity (cf b). (d) Follow-up radiograph obtained 3 weeks later shows a more evident band of new bone formation (arrowheads) corresponding to the abnormality seen at MR imaging.
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Figure 9d. Stress fracture in a 65-year-old man who presented with heel pain after completing a 2-week program of vigorous aerobic exercise. (a) Radiograph shows only a faint sclerotic band in the posterior region of the calcaneus (arrowheads). (b) Sagittal T1-weighted (450/25) MR image shows a low-signal-intensity band in the posterior region of the calcaneus (arrowheads) representing the fracture line. Associated diffuse bone marrow edema of the calcaneus demonstrates ill-defined low signal intensity. (c) Axial T2-weighted (2,500/90) MR image clearly depicts the irregular hypointense fracture line parallel to the posterior cortical margin (arrowheads). The associated diffuse bone marrow edema of the calcaneus has high signal intensity (cf b). (d) Follow-up radiograph obtained 3 weeks later shows a more evident band of new bone formation (arrowheads) corresponding to the abnormality seen at MR imaging.
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Occult Fracture.—As in other bones, MR imaging can help detect radiographically occult fractures of the calcaneus. In such cases, traumatic injury has recently occurred, and MR imaging discloses a fracture line with very low signal intensity associated with cortical interruption as well as signal intensity changes representing edema and medullary hemorrhage.
Bone Bruises
Contusion injuries of bone are thought to represent trabecular microfractures associated with medullary edema and hemorrhage. Radiographic findings are typically normal in these lesions. At MR imaging, the lesions appear as ill-defined reticulated areas confined to the medullary space of cancellous bone, with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images (especially fat-suppressed T2-weighted and STIR images) (24).
Osteomyelitis
The calcaneus is a frequent location of osteomyelitis of the foot in both children and adults. In children, the disease more frequently results from hematogenous spread, whereas in adults it is commonly secondary to spread from a contiguous soft-tissue septic focus in patients with diabetes mellitus, arteriosclerosis, and skin ulcerations. Osteomyelitis of the calcaneus may also be caused by a penetrating wound.
Hematogenous osteomyelitis involving the calcaneus in children shows a predilection for the posterior aspect of the metaphyseal-equivalent region adjacent to the epiphyseal cartilage plate. Foot infection in diabetic patients typically originates at pressure points (eg, the area beneath the calcaneus or metatarsal heads) or in the toes.
MR imaging is useful for defining the extent of osteomyelitis with associated soft-tissue infection and for differentiating soft-tissue infection without osteomyelitis. Osteomyelitis manifests as ill-defined areas of decreased marrow signal intensity on T1-weighted images that increase in signal intensity on T2-weighted or STIR images (Fig 10) (24,25).
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Figure 10a. Osteomyelitis in a 67-year-old diabetic woman. Axial proton-density-weighted (2,500/20) (a) and STIR (2,421/21/160) (b) MR images reveal diffuse alteration in bone marrow signal intensity in the calcaneus corresponding to osteomyelitis. Arrows indicate soft-tissue extension of the infectious process.
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Figure 10b. Osteomyelitis in a 67-year-old diabetic woman. Axial proton-density-weighted (2,500/20) (a) and STIR (2,421/21/160) (b) MR images reveal diffuse alteration in bone marrow signal intensity in the calcaneus corresponding to osteomyelitis. Arrows indicate soft-tissue extension of the infectious process.
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STIR MR imaging is extremely sensitive and may overestimate the true extent of the infection (25). Fat-suppressed gadolinium-enhanced imaging more clearly delineates the extent of infected marrow, which demonstrates enhancement. In cases involving spread from soft-tissue infection, early findings include loss of cortical low signal intensity and edematous changes on the periosteal surface.
Calcaneal Tumors
The calcaneus may be affected by a variety of benign and malignant tumors. Although heel pain is the most frequent early symptom, these lesions are often discovered incidentally at radiography performed after trauma or for vague complaints. In some of these lesions (eg, simple bone cyst, lipoma), MR imaging can provide a specific diagnosis (Figs 11, 12).
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Figure 11a. Lipoma of the calcaneus in a 43-year-old woman. (a) Radiograph shows a well-defined radiolucent lesion in the anterior third of the calcaneus, the region in which a unicameral bone cyst is typically seen. (b) Sagittal T1-weighted (450/25) MR image reveals a focal lesion that is isointense relative to fat with thin, low-signal-intensity margins. This lesion was also isointense relative to fat on T2-weighted and STIR images (not shown), strongly suggesting a diagnosis of calcaneus lipoma.
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Figure 11b. Lipoma of the calcaneus in a 43-year-old woman. (a) Radiograph shows a well-defined radiolucent lesion in the anterior third of the calcaneus, the region in which a unicameral bone cyst is typically seen. (b) Sagittal T1-weighted (450/25) MR image reveals a focal lesion that is isointense relative to fat with thin, low-signal-intensity margins. This lesion was also isointense relative to fat on T2-weighted and STIR images (not shown), strongly suggesting a diagnosis of calcaneus lipoma.
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Figure 12a. Fibrous dysplasia of the calcaneus in a 53-year-old woman. (a) Radiograph shows a radiolucent lesion with sclerotic margins and thick intralesional septations occupying most of the calcaneus. (b) Sagittal T1-weighted (450/25) MR image shows a lesion with low to intermediate signal intensity and hypointense, sclerotic borders. (c) On a sagittal STIR (2,421/20/160) MR image obtained at the same level as b, the lesion has inhomogeneous intermediate to high signal intensity. (d) On an axial proton-density-weighted (2,500/20) MR image, the lesion has intermediate signal intensity. (e) On a corresponding axial T2-weighted (2,500/90) MR image, the signal intensity of the lesion has decreased. The relative hypointensity of the lesion on both T1- and T2-weighted images suggested fibrotic lesional tissue. The diagnosis of fibrous dysplasia was made at bone biopsy.
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Figure 12b. Fibrous dysplasia of the calcaneus in a 53-year-old woman. (a) Radiograph shows a radiolucent lesion with sclerotic margins and thick intralesional septations occupying most of the calcaneus. (b) Sagittal T1-weighted (450/25) MR image shows a lesion with low to intermediate signal intensity and hypointense, sclerotic borders. (c) On a sagittal STIR (2,421/20/160) MR image obtained at the same level as b, the lesion has inhomogeneous intermediate to high signal intensity. (d) On an axial proton-density-weighted (2,500/20) MR image, the lesion has intermediate signal intensity. (e) On a corresponding axial T2-weighted (2,500/90) MR image, the signal intensity of the lesion has decreased. The relative hypointensity of the lesion on both T1- and T2-weighted images suggested fibrotic lesional tissue. The diagnosis of fibrous dysplasia was made at bone biopsy.
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Figure 12c. Fibrous dysplasia of the calcaneus in a 53-year-old woman. (a) Radiograph shows a radiolucent lesion with sclerotic margins and thick intralesional septations occupying most of the calcaneus. (b) Sagittal T1-weighted (450/25) MR image shows a lesion with low to intermediate signal intensity and hypointense, sclerotic borders. (c) On a sagittal STIR (2,421/20/160) MR image obtained at the same level as b, the lesion has inhomogeneous intermediate to high signal intensity. (d) On an axial proton-density-weighted (2,500/20) MR image, the lesion has intermediate signal intensity. (e) On a corresponding axial T2-weighted (2,500/90) MR image, the signal intensity of the lesion has decreased. The relative hypointensity of the lesion on both T1- and T2-weighted images suggested fibrotic lesional tissue. The diagnosis of fibrous dysplasia was made at bone biopsy.
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Figure 12d. Fibrous dysplasia of the calcaneus in a 53-year-old woman. (a) Radiograph shows a radiolucent lesion with sclerotic margins and thick intralesional septations occupying most of the calcaneus. (b) Sagittal T1-weighted (450/25) MR image shows a lesion with low to intermediate signal intensity and hypointense, sclerotic borders. (c) On a sagittal STIR (2,421/20/160) MR image obtained at the same level as b, the lesion has inhomogeneous intermediate to high signal intensity. (d) On an axial proton-density-weighted (2,500/20) MR image, the lesion has intermediate signal intensity. (e) On a corresponding axial T2-weighted (2,500/90) MR image, the signal intensity of the lesion has decreased. The relative hypointensity of the lesion on both T1- and T2-weighted images suggested fibrotic lesional tissue. The diagnosis of fibrous dysplasia was made at bone biopsy.
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Figure 12e. Fibrous dysplasia of the calcaneus in a 53-year-old woman. (a) Radiograph shows a radiolucent lesion with sclerotic margins and thick intralesional septations occupying most of the calcaneus. (b) Sagittal T1-weighted (450/25) MR image shows a lesion with low to intermediate signal intensity and hypointense, sclerotic borders. (c) On a sagittal STIR (2,421/20/160) MR image obtained at the same level as b, the lesion has inhomogeneous intermediate to high signal intensity. (d) On an axial proton-density-weighted (2,500/20) MR image, the lesion has intermediate signal intensity. (e) On a corresponding axial T2-weighted (2,500/90) MR image, the signal intensity of the lesion has decreased. The relative hypointensity of the lesion on both T1- and T2-weighted images suggested fibrotic lesional tissue. The diagnosis of fibrous dysplasia was made at bone biopsy.
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Simple bone cyst is relatively common in the calcaneus. It typically manifests as a well-defined radiolucent lesion in the base of the calcaneal neck, just inferior to the anterior portion of the posterior facet, usually without bone expansion or periostitis. The major differential diagnostic consideration is lipoma, which also occurs in the anterior third to the midportion of the calcaneus. At radiography, lipoma appears as a well-defined radiolucent lesion; unlike with simple bone cyst, however, a central clump of calcification is often observed within the lesion. MR imaging can help establish a confident diagnosis in both simple bone cyst and lipoma: Simple bone cyst has homogeneous low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, whereas lipoma is homogeneously isointense relative to fat with all pulse sequences (Fig 11).
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Bursal Lesions
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Two bursae lie near the insertion of the Achilles tendon on the calcaneus. The retrocalcaneal (subachilleal) bursa is located between the Achilles tendon insertion and the posterior angle of the calcaneus. The retroachilleal bursa is situated between the skin and the Achilles tendon.
At MR imaging, a normal retrocalcaneal bursa manifests as a thin area of high signal intensity on T2-weighted or STIR images. This finding is due to fluid, synovium, or a combination of the two situated deep in relation to the retrocalcaneal fat (26).
Retrocalcaneal Bursitis
Retrocalcaneal bursitis may manifest as an inflammatory arthropathy (rheumatoid arthritis, seronegative spondyloarthropathies), accompany Achilles tendinitis, or occur as an isolated disorder. In the latter case, it is usually a result of repetitive trauma due to athletic overactivity, particularly in runners. Retrocalcaneal bursitis is associated with posterior heel pain made worse by passive dorsiflexion of the ankle. Bursal distention produces tender swelling behind the ankle with bulging on both sides of the tendon.
Initial evaluation of the retrocalcaneal bursa includes radiography, which shows obliteration of normal retrocalcaneal fat, and ultrasonography, which demonstrates a hypoechogenic bursal fluid collection. MR imaging can help establish the diagnosis by showing a bursal fluid collection with low signal intensity on T1-weighted images and with high signal intensity on T2-weighted and STIR images (Fig 13) (3,26). A bursa larger than 1 mm anteroposteriorly, 7 mm craniocaudally, or 11 mm transversely is considered abnormal (26).
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Figure 13. Retrocalcaneal bursitis in a 25-year-old woman. Sagittal STIR (2,421/20/160) MR image shows marked distention of the retrocalcaneal bursa by high-signal-intensity fluid (arrowheads), a finding that represents bursitis. Note also the mild thickening of the Achilles tendon with increased intratendinous signal intensity, a finding that represents tendinitis.
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A diagnosis of associated insertional Achilles tendinitis is clinically significant because local steroid injection may cause tendinous rupture. Rest, activity modification, slight heel elevation with a felt heel pad, and nonsteroidal antiinflammatory drug therapy are sufficient for most patients. A cautious corticosteroid injection into the bursa is sometimes required. Surgical bursectomy and resection of the superior prominence of the calcaneal tuberosity are rarely indicated.
Retroachilleal Bursitis
Retroachilleal bursitis produces a painful, tender subcutaneous swelling overlying the Achilles tendon, usually at the level of the shoe counter. The overlying skin may be hyperkeratotic or reddened. This condition occurs predominantly in women and is generally due to local irritation from the upper edge of a rigid shoe counter. Diagnosis is essentially clinical, and further evaluation is not required.
Retroachilleal bursitis may be discovered incidentally at MR imaging performed to evaluate other heel injuries. Its appearance is similar to that of retrocalcaneal bursitis and consists of a bursal fluid collection just posterior to the distal Achilles tendon with high signal intensity on T2-weighted and STIR images. Treatment consists of rest, heat application, nonsteroidal antiinflammatory drug therapy, padding, and relief from shoe pressure by wearing a soft, nonrestrictive shoe without a counter. Local corticosteroid injection should be avoided. Surgical excision is rarely indicated.
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Tarsal Tunnel Syndrome
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The tarsal tunnel is a fibro-osseous canal that is bounded by the flexor retinaculum superficially and the medial surfaces of the talus and calcaneus on its deep surface. It contains the posterior tibial nerve, the three medial tendons (posterior tibial, FDL, and FDH tendons), and the posterior tibial artery and posterior tibial vein (Fig 14).
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Figure 14a. Normal tarsal tunnel. (a) Oblique axial T1-weighted (500/25) MR image through the midportion of the tarsal tunnel demonstrates that the medial aspect of the talus (T) and calcaneus (C) form the floor of the tarsal tunnel and the flexor retinaculum (fr) forms the roof. The posterior tibial (PT) and FDL (fdl) tendons are seen in the anterior portion of the tarsal tunnel. The medial plantar nerve (MN) is adjacent to the FHL tendon (fhl), whereas the lateral plantar nerve (LN) lies posteriorly. The posterior tibial artery (PTA) and posterior tibial vein (PTV) lie closer to the flexor retinaculum than do the nerves. (b) Oblique axial T1-weighted (500/25) MR image through the inferior portion of the tarsal tunnel shows the medial aspect of the talus (T) and calcaneus (C) forming the floor of the tarsal tunnel, whereas at this level the roof is formed by the abductor hallucis muscle (ab). The transverse interfascicular septum (tis) forms separate upper and lower chambers for the medial and lateral neurovascular bundles, respectively. The medial plantar nerve (mn) lies close to the FHL tendon (fhl), and the medial plantar vascular bundle (mvb) is more superficially located. The lateral plantar nerve (ln) and lateral vascular bundle (lvb) lie between the abductor hallucis and quadratus plantae (qp) muscles. Note the anterior location of the posterior tibial (pt) and FDL (fdl) tendons.
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Figure 14b. Normal tarsal tunnel. (a) Oblique axial T1-weighted (500/25) MR image through the midportion of the tarsal tunnel demonstrates that the medial aspect of the talus (T) and calcaneus (C) form the floor of the tarsal tunnel and the flexor retinaculum (fr) forms the roof. The posterior tibial (PT) and FDL (fdl) tendons are seen in the anterior portion of the tarsal tunnel. The medial plantar nerve (MN) is adjacent to the FHL tendon (fhl), whereas the lateral plantar nerve (LN) lies posteriorly. The posterior tibial artery (PTA) and posterior tibial vein (PTV) lie closer to the flexor retinaculum than do the nerves. (b) Oblique axial T1-weighted (500/25) MR image through the inferior portion of the tarsal tunnel shows the medial aspect of the talus (T) and calcaneus (C) forming the floor of the tarsal tunnel, whereas at this level the roof is formed by the abductor hallucis muscle (ab). The transverse interfascicular septum (tis) forms separate upper and lower chambers for the medial and lateral neurovascular bundles, respectively. The medial plantar nerve (mn) lies close to the FHL tendon (fhl), and the medial plantar vascular bundle (mvb) is more superficially located. The lateral plantar nerve (ln) and lateral vascular bundle (lvb) lie between the abductor hallucis and quadratus plantae (qp) muscles. Note the anterior location of the posterior tibial (pt) and FDL (fdl) tendons.
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In most cases, the posterior tibial nerve divides into its terminal branches, the medial and lateral plantar nerves, within the tarsal tunnel. The origin of the medial calcaneal nerve, which is responsible for the sensitive innervation of the heel, is more variable and can arise directly from the posterior tibial nerve or lateral plantar nerve, occasionally with multiple branches.
Tarsal tunnel syndrome is an entrapment neuropathy of the posterior tibial nerve or of its branches within the tarsal tunnel (27). Clinical manifestations of tarsal tunnel syndrome are variable and depend on the individual nerves damaged and the duration and extent of neural compression. The most common symptoms are pain and paresthesias in the toes, sole, or heel (27). Because of their anatomic variability, the medial calcaneal branches are less commonly involved than the medial and lateral plantar nerves (28); consequently, heel pain is less frequent (27,28). When present, heel pain is usually not isolated (27) but is accompanied by pain in the medial or lateral sole. The main finding at physical examination is the Tinel sign (distal paresthesias produced by percussion over the affected portion of nerve). Electromyography and nerve conduction studies are useful in confirming the diagnosis (27,28).
A number of abnormalities have been described as causing tarsal tunnel syndrome. These include bone deformity after calcaneal fractures, varicosities, tenosynovitis of the flexor tendons, tumors or tumorlike lesions, an accessory or hypertrophied abductor hallucis muscle, and synovial hypertrophy (27,28).
MR imaging clearly depicts the bones, soft-tissue contents, and boundaries of the tarsal tunnel as well as the different pathologic conditions responsible for tarsal tunnel syndrome (Figs 15–17) (28–30).
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Figure 15a. Pigmented villonodular synovitis with involvement of the tarsal tunnel in a 50-year-old man. (a) Sagittal T1-weighted (450/25) MR image shows the relationship of the mass (arrowheads) to the FHL tendon. (b) Sagittal T2-weighted (2,500/90) MR image obtained at same level shows a heterogeneous, predominantly low-signal-intensity lesion occupying the synovial sheath of the FHL tendon (arrowheads).
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Figure 15b. Pigmented villonodular synovitis with involvement of the tarsal tunnel in a 50-year-old man. (a) Sagittal T1-weighted (450/25) MR image shows the relationship of the mass (arrowheads) to the FHL tendon. (b) Sagittal T2-weighted (2,500/90) MR image obtained at same level shows a heterogeneous, predominantly low-signal-intensity lesion occupying the synovial sheath of the FHL tendon (arrowheads).
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Figure 16. Tarsal tunnel syndrome secondary to venous insufficiency in a 68-year-old woman. Axial T2-weighted (2,500/90) MR image through the inferior talocalcaneal portion of the tarsal tunnel in both ankles shows varicose veins occupying the right tarsal tunnel (arrows).
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Figure 17. Tarsal tunnel syndrome secondary to a ganglion in a 34-year-old woman. Sagittal STIR (2,421/ 20/160) MR image through the tarsal tunnel reveals a lobular high-signal-intensity lesion posterior to the FDL tendon in the expected location of the neurovascular bundle (arrows).
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In most cases, MR imaging can also aid in determining whether treatment should be conservative (eg, for proliferative synovitis accompanying rheumatoid arthritis or tenosynovitis) or surgical (eg, for space-occupying lesions). Moreover, MR imaging can aid in surgical planning by indicating the extent of decompression required.
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Heel Fat Pad Abnormalities
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The heel fat pad is normally composed of elastic fibrous tissue septa separating closely packed fat cells. This anatomic architecture acts as a shock absorber at heel strike (5,13).
Heel pain may arise from the fat pad itself. For example, rupture of the fibrous tissue septa, which occurs mainly in obese elderly patients under the influence of ordinary weight bearing or owing to sudden, severe impact, results in attrition of the fat pad with poor stress absorption. These patients experience pain beneath the heel on weight bearing, particularly when standing. Painful heel fat pad is often confused with plantar fasciitis, although it is characterized by tenderness of the posterior weight-bearing portion of the calcaneus, in contrast to the more anterior tenderness associated with plantar fasciitis (5). MR imaging can also help distinguish between these two conditions and in some cases of painful heel fat pad can demonstrate changes in signal intensity, with low-signal-intensity bands representing fibrosis and decreased height of the fat pad.
Fat pad inflammation may also occur in young persons as a result of sports injuries. In such cases, MR imaging demonstrates edematous changes in the fat pad, with ill-defined areas of decreased signal intensity on T1-weighted images that increase in signal intensity on T2-weighted images (31).
MR imaging is also useful in the detection and evaluation of space-occupying lesions within the fat pad (eg, peripheral nerve sheath tumors, rheumatoid nodules) (Figs 18, 19).
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Figure 18a. Schwannoma in a 25-year-old man. (a) Coronal T1-weighted (450/25) MR image shows a well-defined ovoid mass that is isointense relative to adjacent muscle (arrows). (b) On a corresponding coronal gadolinium-enhanced T1-weighted MR image, the lesion demonstrates heterogeneous, predominantly peripheral enhancement with more clearly defined margins (arrows).
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Figure 18b. Schwannoma in a 25-year-old man. (a) Coronal T1-weighted (450/25) MR image shows a well-defined ovoid mass that is isointense relative to adjacent muscle (arrows). (b) On a corresponding coronal gadolinium-enhanced T1-weighted MR image, the lesion demonstrates heterogeneous, predominantly peripheral enhancement with more clearly defined margins (arrows).
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Figure 19a. Rheumatoid nodule in the heel fat pad in a 70-year-old man with long-standing seropositive rheumatoid arthritis. Sagittal T1-weighted (450/25) (a) and STIR (2,421/20/160) (b) MR images show an ill-defined subcutaneous lesion lying just superficial to the plantar fascia (arrows). The lesion has low signal intensity in a and heterogeneous high signal intensity in b. A well-corticated calcaneal spur is also seen.
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Figure 19b. Rheumatoid nodule in the heel fat pad in a 70-year-old man with long-standing seropositive rheumatoid arthritis. Sagittal T1-weighted (450/25) (a) and STIR (2,421/20/160) (b) MR images show an ill-defined subcutaneous lesion lying just superficial to the plantar fascia (arrows). The lesion has low signal intensity in a and heterogeneous high signal intensity in b. A well-corticated calcaneal spur is also seen.
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Subcutaneous rheumatoid nodules are a cardinal diagnostic feature of rheumatoid arthritis, occurring in 20% of patients who test positive for blood rheumatoid factors and rarely in seronegative patients. They usually develop on pressure areas and overlying bony protuberances, most commonly in the olecranon. In the heel, rheumatoid nodules may occur adjacent to the Achilles tendon and in the plantar fat pad. Sometimes these lesions are painful (32); they may also break down and become infected. The MR imaging appearance of heel rheumatoid nodules reflects their histologic composition. Two morphologic patterns have been described at MR imaging. Solid lesions, composed entirely of chronic inflammatory cells and small vessels, have low signal intensity on both T1- and T2-weighted images (Fig 19) and enhance after contrast material injection (32,33). In rheumatoid nodules with central necrosis, the cystic central portion appears hypointense on T1-weighted images and hyperintense on T2-weighted images, whereas the solid peripheral portion, consisting of palisading inflammatory cellular infiltrate, appears hypointense on both T1- and T2-weighted images (32). After contrast material injection, a peripheral rim of enhancement helps demarcate the unenhanced central portion (32).
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Conclusions
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Although not routinely indicated in patients with heel pain, MR imaging is of great value in establishing the diagnosis and in assessing the severity of the disease in ambiguous or clinically equivocal cases. Careful analysis of MR imaging findings and correlation of these findings with patient history and findings at physical examination can suggest a specific diagnosis in most cases. The majority of patients with heel pain can be successfully treated conservatively, but in cases requiring surgery (eg, plantar fascia rupture in competitive athletes, deeply infiltrating plantar fibromatosis, masses causing tarsal tunnel syndrome) MR imaging is especially useful in planning surgical treatment by showing the exact location and extent of the lesion.
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Footnotes
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Abbreviations: FDB = flexor digitorum brevis
FDL = flexor digitorum longus
FHL = flexor hallucis longus
STIR = short-inversion-time inversion recovery
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References
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Abstract
Introduction
